Superabsorbent refers to a water-swellable, water-insoluble, organic or inorganic material capable of absorbing at least about 10 times its weight and up to about 30 times its weight in an aqueous solution containing 0.9 weight percent sodium chloride solution in water. A superabsorbent polymer is a crosslinked neutralized polymer which is capable of absorbing large amounts of aqueous liquids and body fluids, such as urine or blood, with swelling and the formation of hydrogels, and of retaining them under a certain pressure in accordance with the general definition of superabsorbent.
The superabsorbent polymers that are currently commercially available are crosslinked polyacrylic acids or crosslinked starch-acrylic acid graft polymers, in which some of the carboxyl groups are neutralized with sodium hydroxide solution or potassium hydroxide solution. As a result of these characteristic properties, these polymers are chiefly used for incorporation into sanitary articles, such as babies' diapers, incontinence products and sanitary towels.
For fit, comfort and aesthetic reasons and from environmental aspects, there is an increasing trend to make sanitary articles smaller and thinner. This is being accomplished by reducing the content of the high volume fluff fiber of these articles. To ensure a constant total retention capacity of body fluids in the sanitary articles, more superabsorbent polymer content is being used in these sanitary articles. As a result of this, superabsorbent polymers must have increased absorption speed characteristics while retaining other characteristics such as adequate absorption under load and retention capacity.
In future diaper constructions, it is expected there will be less fiber material, or potentially none at all, in the absorber layer to assist in transportation of the liquid or maintenance of an open, fluid permeable structure. The superabsorbent polymer of these future diaper constructions must have a sufficiently high stability in the swollen state, generally called gel strength, so the swollen gel has a sufficient amount of capillary spaces through which liquid can be transported. In addition, the superabsorbent polymers in such diapers must also have a higher absorption rate to maximize the use of available capillary spaces and to compensate for the reduction of typically fast absorbing fibers.
It is therefore an object of the present invention to provide an absorbing polymer composition that exhibits increased rate of water absorption as well as maintaining excellent properties. It is an object to maintain high absorption under load and liquid retention even when the superabsorbent polymer is increased in percent by weight based on the absorbent structure. This can be achieved by increasing the absorption rate of the superabsorbent polymer by increasing the microcellular structure of the polymer.